Ch. 28 Biology

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patterson911
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Ch. 28 Biology
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2010-10-10 17:48:56
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Plants without seeds
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Plants without seeds
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  1. Charophytes
  2. The chlorophytes and charophytes are not the only green algal clades
    • Green Algae-
    • Characteristics
    • · Chlorophylls a and b
    • · Starch storage
    • · Cellulose in cell walls
    • The closest relatives to land plants
    • Key common characteristics with land plants:
    • · Egg retention in the parental organism
    • · Plasmodesmata join the cytoplasm of adjacent cells
    • · Growth is apical (from the tip) and branching
    • · Similar peroxisome content, mechanics of cell division, and chloroplast structure
    • Charophytes live at the margin of marshes and ponds and probably gave rise to the early land plants 400 to 500 million years ago
    • Adaptations to Land
    • Water is difficult to obtain and retain on land
    • Adaptations to land:
    • · Cuticle: hydrophobic, waxy covering that retards water loss
    • · Protected reproductive structures
    • Land plant life cycle—alternation of generation
    • Gametophyte: haploid stage which produces gametes by mitosis
    • Sporophyte: diploid stage which produces spores by meiosis
    • Spores: unicellular dispersal units with thick walls that resist dessication and decay (haploid)
    • Adaptations to life on land distinguish land plants from green algae
  3. Land Plants
  4. Land plants have been divided into 10 major clades
    A major division of the clades is based on whether or not the plants have tracheids—special fluid conducting cells
  5. Nonvascular Land Plants
  6. They are photosynthetic
    • Thought to be similar to the earliest land plants
    • Liverwort : 9,000 species (Marchantia sp.)
    • Moss: 15,000 species (Polytrichum sp.)
    • Hornwort: 100 species (Anthoceros sp.)
    • Short plants – water moves by diffusion
    • Most are terrestrial, growing in dense mats in moist habitats
    • Gametophyte is the dominant generation
    • The sporophyte is dependent on the gametophyte
    • Gametophyte:
    • · Dominant
    • · “nutritionally” independent
    • · Produces haploid gametes by mitosis
    • Fertilization: requires water for sperm movement to eggs
    • Sporophyte:
    • · Protected by the gametophyte
    • - Remains attached
    • - Not “nutritionally” independent
    • · Produces haploid spores by meiosis
    • Spores:
    • · Dispersal unit
    • · Germinate to form a protonema
    • · Protonema grow into a gametophyte
    • What are the differences among clades?
    • Liverworts don’t have stomata
    • Used for gas exchange (and saving water)
    • Another adaptation to life on land!
    • Mosses don’t have a persistently green sporophyte
    • Hornworts do- similar to higher land plants
    • Applications?
    • Nonvasculars are more interesting than economically important
    • Exception: Sphagnum sp. Moss
    • · Dense mats get compressed into peat
    • · Used for fuel
    • · Also very absorbent; used for gardening, field dressing of wounds, and diapers
    • Peat bogs are interesting ecosystems
    • · Acidic
    • · Low oxygen
    • · Slow decomposition
    • · Cover approximately 1% of Earth’s land surface (about half the size of the U.S.)
  7. Seed-less Vascular Plants
  8. Produce vascular tissues, but not seeds
    • Vascular tissues (xylem and phloem) facilitate transport
    • Lignified xylem cells (tracheids) provide rigid structural support
    • Allow for vertical growth!
    • So what?
    • · Compete for sunlight
    • · Disperse spores
    • Another major adaptation of life!
    • Club Mosses – Lycopodium sp. (1,200 species)
    • Horsetails – Equisetum sp (15 species)
    • Whisk Ferns- Psilotum sp. ( 15 species)
    • Ferns – Dryopterus sp. (12,000 species)
    • More vertical and branching growth form
    • More photosynthetic area and spores than un-branched forms
    • Sporophyte is the dominant generation
    • The sporophyte and gametophyte are both independent
    • Notes for 9-23-10
    • Sporophyte:
    • · Dominant
    • · Potentially long-lived
    • · Produces sporangia which produce spores by meiosis
    • · Spores may disperse great distances before germination to form a gametophyte
    • Gametophyte:
    • · Much less noticeable
    • · Short-lived
    • · Produces haploid gametes by mitosis
    • Fertilization:
    • Requires water for sperm movement to eggs
    • Notice that the embryo is still protected as it develops into a sporophyte
    • What are the differences among the seed-less vasculars?
    • Club mosses have microphylls (simple scale-likes leaves)
    • Horsetails have reduced megaphylls that form whorls
    • Whisk ferns have reduced or no megaphylls
    • Ferns have large megaphylls with branching vascular strands
    • Leptosporangiate: lepton = “thin”, referring to sporangia with walls only one cell thick

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